Various electronic devices such as for example frequency converters, rectifiers, and network inverters comprise electronic components for modifying electrical currents and voltages. An electronic component can be for example a controllable power electronic switch such as for example a bipolar junction transistor “BJT”, an insulated gate bipolar transistor “IGBT”, a thyristor, a gate-turn-off thyristor “GTO”, a metal-oxide-semiconductor field-effect transistor “MOSFET”, an Integrated Gate-Commutated Thyristor “IGCT”, or an Injection-Enhanced Gate Transistor “IEGT”. It is also possible that a power electronic switch is a diode in which case the switching operation depends merely on the voltage between the anode and cathode of the diode. When an electronic component conducts electrical current, heat is produced by the internal resistance of the electronic component due to the Joule effect. In electronic components which are used as switches, the momentary heating rate can be especially high during transitions between conductive and non-conductive states. For example, in a transition from the conductive state to the non-conductive state, the internal resistance may have become quite high while the current has not yet decreased. Thus, the heating rate is partly proportional, linearly or non-linearly, to the switching frequency. In electronic components such as e.g. processors, the heating rate is linearly or non-linearly proportional to the clock frequency and the voltage level being used. Increasing the clock frequency means that the internal capacitances of the processor have to be charged and discharged at a higher rate and thus electrical currents which produce heat in the internal resistances of the processer are increased too. Furthermore, increasing the clock frequency or the switching frequency increases the internal effective resistances, and thereby also the heating rate, due to the skin effect.
If the heating rate exceeds the capacity of the available cooling, there is a risk of temperature rise affecting changes in electrical behavior, such that thermal damage could occur in the electronic component under consideration. Therefore, it is important to manage the electrical current of the electronic component so that the heating rate does not exceed the capacity of the cooling. The management of the electrical current may comprise for example short-circuit “SC” protection, control of high frequency components of the electrical current by limiting the switching frequency so as to limit switching losses, management of thermal cycling of an electronic component, reducing the clock frequency of a processor or the like so as to limit electrical currents, and/or balancing of electrical currents of parallel connected electronic components.
The above-mentioned management of the electrical current needs measured information which is directly or indirectly indicative of the heating rate in the electronic component. One conventional technique for measuring the heating rate includes integration of the product of instantaneous values of measured voltage and electrical current. Another conventional technique for measuring the heating rate includes measuring surface temperature from one or more measuring points on the surface of the electronic components. These techniques are, however, not free from challenges. The technique based on the product of the instantaneous values of the voltage and the electrical current requires highly accurate high bandwidth voltage and current sensors where a phase shift between indicated and real voltages and a phase shift between indicated and real electrical currents are sufficiently close to each other in order that the product of the voltage and the electrical current would represent the instantaneous power at a sufficient accuracy. The voltage and current measurements may be challenging to be carried out with a sufficient accuracy especially when the switching frequency of the electronic component is on the range from hundreds of kHz to few MHz. Challenges related to the technique based on the measured surface temperatures are that the junction temperature of the electronic component can be at least occasionally significantly higher than the surface temperatures and that the measured surface temperatures follow the junction temperature with a delay. Therefore, e.g. short-circuit protection based on the measured surface temperatures can be too slow for being able to protect the electronic component. A further challenge for both of the above-mentioned techniques is that those cannot observe the temperatures of individual semiconductor chips in a case where an electronic component is a module type component that contains multiple chips connected in parallel and/or in series. Due to different thermal impedances for different chips and/or due to differences in parasitic inductances and/or resistances concerning different chips, the heat generation and temperatures are generally not the same for every chip.